ok first a little background on the bike: motor is in a custom frame, exhuast choped but O2 sensor still plugged in, but no ex. valve, no airbox, independent uni filters, air temp sensor still plugged in and i think thats it, any other Q's i should be able to answer. im getting ready to buy the bike but he says that the bike develoved a midrange "hicup" in the last 2 races. bike is used in dirtbike hillclimbs. and here is a link to a video i shot of the bike with the hicup. http://www.youtube.com/watch?v=6GVWy1bLGXQ
it doesnt have a power commander. you can see in the beggining of the run its running real real rough then it clears up a bit. another run it looked like just about the whole run it was running real rough then it cleared near the top and just took off.
what do you guys think it could be?

 

I don't have an answer to you, but that video is badass.

 

Wouldn't surprise me if the motor doesn't like being ridden hard and put away wet.

 

mabey its just tuned wrong (or not at all, like you said there is no PC), that much work done to the intake and exhaust with out tune would probably throw things off a bit. (people tune bikes with just a slip on and a new air filter)

when you say chopped exhaust do you mean no can? just strait pipe after the headers? mabey the chopped exhaust is not helping exhaust scavenging/back pressure, which important for low end (i know very little about that so look it up, but it does matter)

 

what really gets me is that he said it didnt start doing it till the last to races, and that its only under load, once it hits the high rps and gets the tire spinning its all good. i will try taking a look inside the service manual and see if has any of those symptoms but well see. dont forget i have that video of it at the top you can listen to.
thanks

 

no one has any ideas?? mabe a throttle position sensor?